Investigating the Kinetics of Polymerization Required for Bulk-Mediated Alignment of Liquid Crystal Elastomers

Liquid crystal elastomers (LCEs) are lightly cross-linked polymer networks that exhibit liquid crystal order combined with rubber elasticity. LCEs are thermally responsive and if well aligned, they can elongate by over 300% when transitioning from the isotropic (unaligned) to nematic (aligned) state. Previous approaches to induce alignment restrict the LCEs to thin films with limited geometries. For expanded applications, more geometries are desired. This study presents a strategy for developing bulk-mediated alignment of LCEs utilizing the photodimerization of poly (vinyl cinnamate) during simultaneous polymerization via a base-catalyzed thiol-acrylate Michael addition (TAMA) reaction. It is expected that the alignment process will be sensitive to an assortment of reaction conditions and rates, and therefore, the foundational TAMA reaction must be thoroughly investigated. Experiments with varying amounts and types of catalysts and reagents were monitored using time resolved FT-IR spectroscopy. It was found that the rate of the reaction increases and then saturates when catalyst concentration is increased. Preliminary data suggests that the cinnamate pendants dimerize in the system when irradiated with UV light, but more experiments are needed in order to demonstrate the viability of bulk-mediated alignment. If successful, this alignment technique may be instrumental in developing responsive elastomers having complex three dimensional geometries with applications ranging from rewritable braille to soft muscle actuators.